Friction feeders are known in the art. As the name suggests, a friction feeder relies on the interaction of several components around the exit nip of the feeder that results in the singulation of paper documents in a paper stack. The common components in most friction feeders are the driving mechanism to drive a sheet of paper document out of the exit nip and the retarding element to retain all the other sheets in the stack so as to prevent multiple feeds. To provide the necessary friction for retaining the other sheets in the stack, the surface of the retarding element is usually made of an elastomeric material or a hard, rough coating. Ifkovits, Jr. et al. (U.S. Pat. No. 5,294,102, hereafter referred to as Ifkovits) discloses a friction feeder wherein the surface of the retarding element is coated with tungsten carbide grit. Godlewski (U.S. Pat. No. 4,666,140) discloses a friction feeder wherein the surface of the retarding element is made of an elastomeric-like material. Green (U.S. Pat. No. 5,244,198) discloses a friction feeder wherein the retarding element is a continuous belt made of an elastomeric material mounted on a pair of rollers. A friction feeder can be designed to operate as a top feeder or a bottom feeder. The above-mentioned friction feeders are bottom feeders, wherein the sheets in a generally vertical stack are moved out the stack, one at a time, by a driving mechanism below the stack. A typical friction feeder is shown in FIG. 1. As shown, the feeder 1 uses a driving mechanism 30 to drive the bottom sheet 10 of a stack 20 out of the exit nip 64 and a retarding element 40 (a cylindrical member) to hold back the other bottom sheets. In general, the retarding element 40 has a relatively large diameter at the exit nip so that a number of sheets at the bottom of the stack can fan out to follow the surface curvature of the retarding element, forming a singulated stack portion 24. In the singulated portion, the sheets are slightly separated from each other in that the leading edge of one sheet is positioned slightly ahead of the sheets above. As shown in FIG. 1, the driving mechanism 30 comprises a continuous belt 32 mounted on a pair of rollers 34. However, the driving mechanism can simply be rollers with a resilient surface.
In order for the retarding element 40 to be effective in preventing other bottom sheets from being pulled out by the driving mechanism 30 along with the bottom sheet 10, the retarding element 40 must have a high friction surface 50 which is fixedly mounted on a roller 42. In operation, the high friction surface 50 is stationary relative to the moving sheet 10. The friction between the bottom sheet 10 and the sheet 10′ above is lower than the friction between the retarding surface 50 and a sheet 10′. If the surface 50 of the retarding element 40 is coated with a layer of hard grit, as disclosed in Ifkovits, paper dust will accumulate at the surface section 52 at the feed zone 62 where the sheets in the singulated portion 24 are retained by the retarding element 40 when the bottom sheet 10 is driven out of the exit nip 64. After extensive use, the surface roughness is reduced mainly because of the accumulated paper dust, thereby reducing the effectiveness of the retarding surface 50. If the surface 50 of the retarding element 40 is made of an elastomeric material, as disclosed in Green and Godlewski, the contact between the sheets and the retarding surface 50 at the feed zone 62 will wear out the contact surface section 52, changing the retard characteristics of the elastomeric surface.
In order to provide an unworn portion of the retarding surface to the exit nip, Green uses a locking mechanism to keep the retarding surface stationary in operation. When it is necessary to rotate the retarding surface to provide an unworn portion at the exit nip, the operator loosens the locking mechanism and manually repositions the retarding surface. This manual method of furnishing an unworn portion of the retarding surface is inconsistent and inconvenient.
Thus, it is advantageous and desirable to provide a method and device for rotating the retarding surface in a simple and consistent fashion.